Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.41   8.319%   $73.0178   $73.02   $73.00   $73.00  
  Purchase #2 $195.70   5.493%   $206.4498   $206.45   $206.45   $206.40  
  Purchase #3 $113.39   5.136%   $119.2137   $119.21   $119.20   $119.20  
  Purchase #4 $216.42   12.585%   $243.6565   $243.66   $243.65   $243.70  
  Purchase #5 $160.71   12.691%   $181.1057   $181.11   $181.10   $181.10  
  Purchase #6 $235.99   5.686%   $249.4084   $249.41   $249.40   $249.40  
  Purchase #7 $5.80   9.145%   $6.3304   $6.33   $6.35   $6.30  
  7 purchase totals = $995.42       $1,079.1823   $1,079.19   $1,079.15   $1,079.10